Posted by: Mudassir Ali | July 21, 2010

Using Call Flows to Resolve Call Processing Problems

http://www.cisco.com/iam/unified/ipt611/Using_Call_Flows_to_Resolve_Call_Processing_Problems.htm

Using Call Flows to Resolve Call Processing Problems

This topic provides information about a typical call flow in an IP telephony environment. Figure 1 shows a call flow that illustrates the actions in a typical call between the following devices at two different sites:

Cisco Unified IP Phone (SCCP)

Cisco Unified Communications Manager

Gatekeeper

Figure 1 Call Flow in an IP Telephony Environment

Figure 2 Call Flow in an IP Telephony Environment (continued)

Figure 3 Call Flow in an IP Telephony Environment (continued)

Figure 4 Call Flow in an IP Telephony Environment (continued)

Figure 5 Call Flow in an IP Telephony Environment (continued)

For both successful and unsuccessful calls, an industry-standard cause code value appears in the disconnect or release signaling messages. The cause code reveals if the call was disconnected normally (typically cause code 16) or abnormally. Table 1 lists the standard cause values that may appear in the trace files as part of disconnect processing.

Table 1 Disconnect Cause Code Values
Hexadecimal Code with High-Order Bit Set Hexadecimal Code Without High-Order Bit Set Decimal Code Description
0x81 0x01 1 Unallocated (unassigned) number. This cause indicates that the destination requested by the calling user cannot be reached because the number is unassigned. This number is not in the routing table, or it has no path across the ISDN network.
0x82 0x02 2 No route to specified transit network (National use). This number was dialed with a transit network code such as 108880 to go from AT&T and MCI, and there is no route across. The wrong transit network code was dialed.
0x83 0x03 3 No route to the destination. The dialed number is in the routing plan, but there is no physical route to the destination. The most likely cause of this is that the PRI D-channel is down, or the span or WAN is not connected correctly.
0x84 0x04 4 Send special information tone.
0x85 0x05 5 Misdialed trunk prefix (National use).
0x86 0x06 6 Channel unacceptable.
0x87 0x07 7 Call awarded and being delivered in an established channel.
0x88 0x08 8 Preemption.
0x89 0x09 9 Preemption. Circuit reserved for reuse.
0x90 0x10 16 Normal call clearing. This is one of the most common codes and is received for many reasons. It usually occurs because someone hung up the call.
0x91 0x11 17 User busy. The number dialed is busy and cannot receive any more calls.
0x92 0x12 18 No user responding. The number that is being dialed has an active D-channel, but the far end chooses not to answer.
0x93 0x13 19 No answer from the user (user alerted). The number that is being dialed has an active D-channel, but the far end chooses not to answer.
0x94 0x14 20 Subscriber absent.
0x95 0x15 21 Call rejected.
0x96 0x16 22 Number changed. This cause code is generated when a subscriber on the PSTN has changed his or her phone number. Usually this message is accompanied by a progress indicator stating that in-band information is available. The PSTN provides an announcement in-band indicating the new phone number, if available.
0x9A 0x1A 26 Nonselected user clearing.
0x9B 0x1B 27 Destination is out of order. The number dialed is a working number, but the span is not active.
0x9C 0x1C 28 Invalid number format (address incomplete). This can happen when you are calling out using a network type number (enterprise) when you should be calling out Unknown or National.
0x9D 0x1D 29 Facility rejected.
0x9E 0x1E 30 Response to STATUS ENQUIRY.
0x9F 0x1F 31 Normal, unspecified. This is another common code. It happens when the network cannot determine what to do with the call being made.
0xA2 0x22 34 No circuit/channel is available. No B-channels are available to make the selected call.
0xA6 0x26 38 Network is out of order.
0xA7 0x27 39 Permanent frame mode connection is out of service.
0xA8 0x28 40 Permanent frame mode connection is operational.
0xA9 0x29 41 Temporary failure. The call was disconnected due to a network failure. This code appears for some long distance providers if the hunt sequence is incorrect. PRI lines must be set up for a flex hunt sequence (not a float hunt sequence).
0xAA 0x2A 42 Switching equipment congestion.
0xAB 0x2B 43 Access information discarded. Usually reported when the far-end ISDN switch removes some piece of information before tandem-switching a call. For example, some PBXs strip the display IE before sending a call out toward the PSTN and send back a message with this cause code.
0xAC 0x2C 44 Requested circuit/channel is unavailable. This happens when you get in a glare condition: Both sides are selected top-down or bottom-up. Change the Allocation Direction (so that one end is top-down and the other is bottom-up).
0xAE 0x2E 46 Precedence call blocked.
0xAF 0x2F 47 Resource unavailable, unspecified. Whenever you see Cisco Unified Communications Manager initiate a disconnect with cause code 0xAF, 99% of the time the problem is related to a media setup failure. Check for codec capabilities mismatches, especially your regions configuration.
0xB1 0x31 49 Quality of service unavailable.
0xB2 0x32 50 Requested facility not subscribed. This code typically indicates you are trying to use a service you are not permitted to use. For example, you might be trying to make a voice call on an ISDN circuit provisioned for data only.
0xB5 0x35 53 Outgoing calls barred within Closed User Group (CUG).
0xB7 0x37 55 Incoming calls barred within CUG.
0xB9 0x39 57 Bearer capability not authorized. This code indicates that you are placing a call with a bearer capability you are not allowed to use.
0xBA 0x3A 58 Bearer capability not presently available. This code indicates that you are placing a call with a bearer capability for which the service provider does not currently have capacity to supply.
0xBE 0x3E 62 Inconsistency in designated outgoing access information and subscriber class.
0xBF 0x3F 63 Service or option unavailable, unspecified.
0xC1 0x41 65 Bearer capability not implemented. The cause could be one of the following occurrences:•You need to change the PCM Type value to the setting appropriate for your country. This is the most common cause, especially in countries where G.711 A-law companding is the standard. If your gateway is configured for µ-law and the service provider or PBX is expecting A-law, you will see calls disconnected with this cause code.

The central office (CO) does not understand an information element in the setup message.

You are connected to a PBX and you are sending out a network type number when the switch accepts only Unknown or National.

You are selecting European PRI and you have the progress indicators turned on when they should be off.

0xC2 0x42 66 Channel type not implemented.
0xC5 0x45 69 Requested facility not implemented.
0xC6 0x46 70 Only restricted digital information bearer capability is available (National use).
0xCF 0x47 79 Service or option not implemented, unspecified.
0xD1 0x51 81 Invalid call reference value. This code indicates that the far-end switch did not recognize the call reference for a message sent by the gateway.
0xD2 0x52 82 Identified channel does not exist. This code indicates a call attempt on a channel that is not configured on the far end. This could happen if you are using a fractional PRI. As of Cisco Unified Communications Manager Release 3.3, fractional PRIs are no longer supported.
0xD3 0x53 83 A suspended call exists, but this call identity does not.
0xD4 0x54 84 Call identity in use.
0xD5 0x55 85 No call suspended.
0xD6 0x56 86 Call having the requested call identity has been cleared.
0xD7 0x57 87 User is not a member of CUG.
0xD8 0x58 88 Incompatible destination. The cause could be one of the following occurrences:•The number being dialed is not capable of the type of call.

You are calling a restricted line in unrestricted mode.

You are calling a POTS phone using unrestricted mode.

0xDA 0x5A 90 Nonexistent CUG.
0xDB 0x5B 91 Invalid transit network selection (National use).
0xDF 0x5F 95 Invalid message, unspecified.
0xE0 0x60 96 Mandatory information element is missing. The far-end switch states that a message was received missing an information element it considers to be mandatory per the Q.931 specification.
0xE1 0x61 97 Message type nonexistent or not implemented.
0xE2 0x62 98 Message is incompatible with the call state, or the message type is nonexistent or not implemented. This code is usually indicative of an ISDN protocol mismatch. Each ISDN protocol variant has a slightly different state machine based on the state machines defined in the Q.931 specification. If the two sides of an ISDN connection are not configured for the same protocol, one side might violate the other’s call state machine. If an ISDN message is sent that is not expected in the current call state, this cause is generated.
0xE3 0x63 99 An information element or parameter does not exist or is not implemented.
0xE4 0x64 100 Invalid information element contents. The cause could be one of the following occurrences:•The call has an information element that is not understood by the switch being called. The E4 is usually followed by the information element that is causing the problem.

The most common problem is that you are trying to place a call using a network number when the switch being called accepts only National, International, or Unknown dialing.

This code is also generated when you are using Network-Specific Facilities as an element when they are not needed.

0xE5 0x65 101 The message is incompatible with the call state. This code is usually indicative of an ISDN protocol mismatch. Each ISDN protocol variant has a slightly different state machine based on the state machines defined in the Q.931 specification. If the two sides of an ISDN connection are not configured for the same protocol, one side might violate the other’s call state machine. If an ISDN message is sent that is not expected in the current call state, this cause is generated.
0xE6 0x66 102 Recovery on timer expiry. This occurs when ISDN messages don’t arrive in specified time according to the Q.931 specification. The E6 is sometimes followed by the timer that has expired (for example, 03 01 00—the 310 timer).
0xE7 0x67 103 Parameter nonexistent or not implemented—passed on (National use).
0xEE 0x6E 110 Message with unrecognized parameter discarded.
0xEF 0x6F 111 Protocol error, unspecified.
0xFF 0x7F 127 Interworking, unspecified.
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